1,3,3-Trimethyl-1-(aminomethyl)-5-aminocyclohexane (hereinafter referred to as “isophoronediamine” or “IPDA”) is an industrially important compound to be used as a raw material for e.g., epoxy curing agents and polyurethanes. An isophoronediamine has two isomers, i.e., a cis-isomer and a trans-isomer, derived from a cyclohexane ring. It is known that the physical properties of a polymer obtained by using an isophoronediamine vary depending upon the ratio of isomers, a cis-isomer and a trans-isomer.
For example, in an epoxy resin obtained by using an isophoronediamine having a high trans-isomer content as a curing agent, extension of pot life and a decrease in maximum peak exothermic temperature are observed. In contrast, in an epoxy resin obtained by using an isophoronediamine having a high cis-isomer content as a hardener, the reaction rate is reported to be extremely high (Patent Document 1).
For these reasons, it is extremely important to control the isomer ratio of an isophoronediamine. Various methods have been proposed for controlling the isomer ratio of an isophoroediamine.
For example, as a method for controlling the isomer ratio, a method of controlling hydrogenation conditions of a precursor of an isophoroediamine, i.e., 3-cyano-3,5,5-trimethylcyclohexanone, to control a cis/trans ratio of the resultant isophoronediamine is reported (Patent Document 2, Patent Document 3).
Since a trans-isophoronediamine has a lower boiling point than a cis-isophoronediamine, the isomer ratio can be varied by distillation (Patent Document 4).
Further, as a method for isomerizing an isophoronediamine, a method for isomerizing a trans-isophoronediamine or a cis-isophoronediamine in the presence of a metal catalyst is reported (Patent Document 5).